1. Field of the Invention
The present invention relates to a slim mobile communication device and a related antenna structure and, more particularly, to a slim mobile communication device and a related antenna structure having a wireless wide area network (WWAN) antenna that is tightly coupled to a neighboring system ground plane.
2. Description of the Related Art
With developments in mobile communication devices, a built-in antenna of a mobile communication device is not only required to satisfy the operating bands of the wireless wide area network (at least 824˜960 MHz and 1710˜2170 MHz), but also required to have close integration between the built-in antenna and a system ground plane in order to make effective use of the interior space of the mobile communication device. Therefore, the built-in antenna of the mobile communication device must be designed not only to be light and slim, but also to be tightly coupled to the system ground plane. Furthermore, in order to have wideband operating capabilities, the antenna is usually disposed at a no-ground portion to have a lower Q value and is able to cover five operating bands of WWAN (i.e., 824˜960 MHz and 1710˜2170 MHz). Then the antenna can form a planar structure on the no-ground portion to decrease the height of the antenna disposed on the system circuit board and be applied to a slim mobile communication device.
However, a side edge of the antenna designed by the method above, especially a side edge comprising the end terminal of the antenna, must have a clearance distance to the ground plane to decrease the effects on the performances of the antenna. As a result, the antenna needs a larger no-ground portion, and the size of the ground portion of the mobile communication device will hence be decreased. Therefore, the arrangement of the associated electronic components to be disposed on the ground portion of the mobile communication device will be affected.
A planar antenna in the prior art, disclosed in U.S. public US 2009/0273521 A1 “Coplanar Coupled-fed multiband antenna for the mobile device,” is applied for WWAN operation and is disposed on a no-ground portion. However, the no-ground portion in the prior art is separated from the system ground plane by a linear or straight edge and cannot be tightly coupled to the system ground plane. In order to be tightly coupled to the system ground plane, at least two edges of the no-ground portion should be surrounded by the neighboring system ground plane. Therefore, although the antenna is capable of wideband operation, the antenna needs a larger no-ground portion, and the arrangement of the interior space of the mobile communication device will be affected.
Therefore, it is desirable to provide a slim mobile communication device to mitigate and/or obviate the aforementioned problems.